Removal of emerging pollutants by a 3-step system: Hybrid digester, vertical flow constructed wetland and photodegradation post-treatments.

The removal of emerging pollutants from municipal wastewater was studied for the first time using a three-step pilot-scale system: 1) hybrid digester (HD) as first step, 2) subsurface vertical flow constructed wetland (VF) as second step, and 3) photodegradation (PD) unit as third step or post-treatment. The HD and VF units were built and operated in series with effluent recirculation at pilot scale. For the PD post-treatment, three alternatives were studied at lab-scale, i) UVC irradiation at 254 nm (0.5 h exposure time), ii) UVA irradiation at 365 nm using a TiO2-based photocatalyst and iii) sunlight irradiation using a TiO2-based photocatalyst, the last two for 1 and 2 h. Alternative iii) was also tested at pilot-scale. Degradation of nine compounds was evaluated: acetaminophen (ACE), caffeine (CAF), carbamazepine (CBZ), ketoprofen (KET), ibuprofen (IBU), diclofenac (DCL), clofibric acid (ACB), bisphenol A (BPA), and sotalol (SOT). Overall, the HD-VF-UVC system completely removed (>99.5 %) ACE, CAF, KET, IBU, DCL and ACB, and to a lesser extent SOT (98 %), BPA (83 %) and CBZ (51 %). On the other hand, the HD-VF-UVA/TiO2 system (at 2 h) achieved >99.5 % removal of ACE, CAF, KET, IBU and DCL while ACB, BPA, CBZ and SOT were degraded by 83 %, 81 %, 78 % and 68 %, respectively. Working also at 2 h of exposure time, in summer conditions, the HD-VF-Sol/TiO2 system achieved >99.5 % removal of ACE, CAF, KET, IBU, DCL and ACB, and to a minor extent BPA (80 %), SOT (74 %) and CBZ (69 %). Similar results, although slightly lower for SOT (60 %) and CBZ (59 %), were obtained in the pilot sunlight plus TiO2 catalyst unit. However, the use of sunlight irradiation with a TiO2-based photocatalyst clearly showed lower removal efficiency in autumn conditions (i.e., 47 % SOT, 31 % CBZ).

Erratum: Canle, M., et al. Improved Photocatalyzed Degradation of Phenol, as a Model Pollutant, over Metal-Impregnated Nanosized TiO2. Nanomaterials 2020, 10, 996.

The authors wish to make the following corrections to this paper: [...].

Improved Photocatalyzed Degradation of Phenol, as a Model Pollutant, over Metal-Impregnated Nanosized TiO2.

Photocatalyzed degradation of phenol in aqueous solution over surface impregnated TiO2 (M = Cu, Cr, V) under UV-Vis (366 nm) and UV (254 nm) irradiation is described. Nanosized photocatalyts were prepared from TiO2-P25 by wet impregnation, and characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy, and adsorption studies. No oxide phases of the metal dopants were found, although their presence in the TiO2-P25 lattice induces tensile strain in Cu-impregnated TiO2-P25, whereas compressive strain in Cr- and V-impregnated TiO2-P25. Experimental evidences support chemical and mechanical stability of the photocatalysts. Type IV N2 adsorption-desorption isotherms, with a small H3 loop near the maximum relative pressure were observed. Metal surface impregnated photocatalysts are mesoporous with a similar surface roughness, and a narrow pore distribution around ca. 25 Å. They were chemically stable, showing no metal lixiviation. Their photocatalytic activity was followed by UV-Vis spectroscopy and HPLC-UV. A first order kinetic model appropriately fitted the experimental data. The fastest phenol degradation was obtained with M (0.1%)/TiO2-P25, the reactivity order being Cu > V >> Cr > TiO2-P25 under 366 nm irradiation, while TiO2-P25 > Cu > V > Cr, when using 254 nm radiation. TOC removal under 366 nm irradiation for 300 min showed almost quantitative mineralization for all tested materials, while 254 nm irradiation for 60 min led to maximal TOC removal (ca. 30%). Photoproducts and intermediate photoproducts were identified by HPLC-MS, and appropriate reaction pathways are proposed. The energy efficiency of the process was analysed, showing UV lamps are superior to UVA lamps, and that the efficiency of the surface impregnated catalyst varies in the order Cu > V > Cr.

On the kinetics and energetics of one-electron oxidation of 1,3,5-triazines.

One-electron oxidation of 1,3,5-triazines is observed with both excited uranyl ion (*UO2(2+)) and sulfate radical anion (SO4.-) in aqueous solution, but not with Tl2+, indicating that the standard reduction potentials E degree of 1,3,5-triazine radical cations are = 2.3 +/- 0.1 V vs. NHE, consistent with theoretical calculations; this suggests that if triazines inhibit electron transfer during photosynthesis, they would need to act on the reductive part of the electron transport chain.